Test-retest reliabilty of exercise-induced hypoalgesia after aerobic exercise

Objective: Exercise increases pressure pain thresholds (PPTs) in exercising and nonexercising muscles, known as exercise-induced hypoalgesia (EIH). No studies have investigated the test-retest reliability of change in PPTs after aerobic exercise. Primary objectives were to compare the effect on PPTs after an incremental bicycling exercise compared with quiet rest and to investigate the relative and absolute test-retest reliability of the test stimulus (PPT) and the absolute and relative EIH response in exercising and nonexercising muscles. Setting: Laboratory. Methods: In two sessions, PPTs in the quadriceps and trapezius muscles were assessed before and after 15 minutes of quiet rest and 15 minutes of bicycling in 34 healthy subjects. Habitual physical activity was assessed by the International Physical Activity Questionnaire (IPAQ). Results: Bicycling increased PPTs in exercising and nonexercising muscles in both sessions (P < 0.05). The magnitude of the EIH response in the exercising muscle was, however, larger in the second compared with the first session (P < 0.015). PPTs showed excellent (intraclass correlation [ICC] ≥ 0.84) within-session and between-session test-retest reliability. The EIH response in exercising and nonexercising muscles demonstrated fair (ICC = 0.45) between-session relative test-retest reliability, but agreement in EIH responders between sessions was not significant (quadriceps: κ = 0.24, P = 0.15; trapezius: κ = 0.01, P = 0.97). Positive correlations between the IPAQ score and PPTs were found (quadriceps: r = 0.44, P = 0.009; trapezius: r = 0.31, P = 0.07) before exercise. No significant association was found between IPAQ and EIH. Conclusions: Incremental bicycling exercise increased PPTs with fair relative and absolute reliability of the EIH response. These data might have an impact on future studies investigating EIH and for clinicians designing exercise programs for pain relief.